This invention relates generally to ignition analyzers for automotive engines and particularly to an interface unit for coupling an ignition analyzer, such as the Sun Electric Corporation Model MCA 3000, to automotive engines having distributorless ignition systems.
In distributorless ignition systems, individual pairs of spark plugs are connected by a common ignition coil and are fired simultaneously, with one spark plug firing resulting in a real firing event and the other plug firing resulting in a wasted firing event. The real firing event occurs on the compression stroke. The wasted firing event occurs on the exhaust stroke and contributes no power to the engine. With the arrangement, a single ignition coil is used for each pair of spark plugs which are fired with opposite polarity voltages. The voltage during the wasted firing event is typically one third of the real firing event voltage. For a four cylinder engine, two individual ignition coils are required and for a six cylinder engine, three are required. A major difficulty is that it is not readily known whether a spark plug experiences a real firing event or a wasted firing event since each spark plug is fired during both the compression and the exhaust strokes of each engine cylinder cycle. The above-mentioned U.S. Pat. No. 5,068,613 describes a system that determines the real and wasted firing events by using a pair of pickup clamps, each of which is coupled to the spark plug wires having secondary voltages of like polarity, in conjunction with a #1 cylinder secondary pickup clamp.
Difficulties often arise because of the crowded conditions under the hood of a modern day automobile and because of the engine design. Often it is not possible to access all of the spark plug wires of like polarity with a single pickup clamp. In the system described in U.S. Pat. No. 5,068,613 No. mentioned above, the two pickup clamps are designed to couple spark plug wires having the same signal polarity. In an automobile engine where that is physically impossible with the pickup clamps, the invention in copending application Ser. No. 651,677 solves the need.
With that invention, the engine type is entered into the interface unit via a keypad. A so-called vehicle personality module or card is installed to interconnect with the vehicle connector. The personality module provides level matching for signals going between the vehicle and a logic cell array (LCA). The LCA is in communication with a ROM memory that stores spark plug polarity and pattern information for a variety of different engines, configures a solid state input switch such that an appropriate polarity signal is outputted for a particular spark plug wire, irrespective of the signal input polarity received by the signal pickup clamp. The particular wires that are to be grouped in each pickup clamp are identified for the technician via a display device. A #1 cylinder pickup clamp is installed on the #1 cylinder spark plug wire and provides #1 cylinder clock information to the LCA. In situations where the #1 cylinder spark plug wire is inaccessible, the operator may select any other cylinder to trigger on. This is accomplished via a keypad entry. As mentioned, in accordance with U.S. Pat. No. 5,068,613, the secondary signals are sorted into wasted and real firing event groups and the real firing event (power) #1 signal is determined. Thus the interface of that invention permits the engine analyzer to be used with distributorless ignition systems of many different types.
The present invention is specifically concerned with performing, in a fairly rapid manner, secondary only tests on an engine. Often such tests are sufficient to determine engine operating conditions without requiring detailed under-the-hood hook ups and specialized engine information. In such a test, the vehicle connector and the personality module are not used. Consequently, there is no primary clock signal, such as an "EST" or "spout" signal, to drive the LCA logic array. The present invention derives a "pseudo" primary clock from the secondary waveforms for driving the LCA logic to determine the real and the wasted firing event secondary signals.